US 4360883 A Abstract Out of nine equal square picture cells forming a picture, only four picture cells surrounding the central picture cell which is to be restored by estimation are utilized. The central picture cell is divided into four equal square sub-cells. The densities of the sub-cells are determined from the mutual relations between the central picture cell and the four surrounding picture cells to determine the density of the central picture cell.
Claims(2) 1. A method of restoring a picture cell by estimation which comprises the steps of:
sampling a picture to obtain a plurality of equal size square picture cells as samples; selecting a picture cell to be restored; determining the optical density (S _{3}) of said picture cell to be restored;determining the optical densities of four picture cells which are adjacently positioned above, below, at the left side, and at the right side of the picture cell to be restored, said optical densities being represented by the values S _{1}, S_{5}, S_{2} and S_{4} respectively;dividing said picture cell to be restored into four equal sized square sub-cells, said four sub-cells being identified as upper left, upper right, lower left, and lower right; determining estimated optical densities O _{1}, O_{2}, O_{3} and O_{4} for said four sub-cells from mutual relationships between the optical density (S_{3}) of said picture cell to be restored and the optical densities (S_{1}, S_{5}, S_{2} and S_{4}) of said four picture cells adjacently positioned about said picture cell to be restored, the optical density of said upper left sub-cell being represented by O_{1}, the density of said upper right sub-cell being represented by O_{2}, the density of said lower left sub-cell being represented by O_{3}, and the density of said lower right sub-cell being represented by O_{4} ;outputting by means of a decoder a first control signal to generate a black picture cell when the value of each of said estimated optical densities is 1; outputting by means of said decoder a second control signal to generate a white picture cell when the value of each of said estimated optical densities is 0; and outputting by means of said decoder a third control signal to generate at least one black sub-cell which has an estimated optical density of 1 and to generate white sub-cells for the remainder of said sub-cells which remainder of said sub-cells have an estimated optical density of 0. 2. A method of restoring a picture cell by estimation as recited in claim 1 wherein said step of determining the estimated optical densities for said four sub-cells comprises the steps for:
quantizing the optical density (S _{3}) of said picture cell to be restored into one of five levels (quinary quantization) such that said quantized value (S^{q} _{3}) is represented as one of the numbers 1/5, 2/5, 2/5, 4/5 and 5/5;analyzing the results of said quantization as follows: when S ^{q} _{3} =1/5, then O_{1} =O_{2} =O_{3} =O_{4} =0, andwhen S ^{q} _{3} =5/5, then O_{1} =O_{2} =O_{3} =O_{4} =1wherein 0 represents white and 1 represents black; further analyzing the results of said quantization for the condition S/5<S ^{q} _{3} <4/5 as follows:when S ^{q} _{3} =2/5, then O_{l} =1 and O_{j} =O_{k} = O_{l} =0when S ^{q} _{3} =3/5, then O_{i} =O_{j} =1 and O_{k} =O_{l} =when S ^{q} _{3} =4/5, then O_{i} =O_{j} =O_{k} =1 and O_{l} =0wherein O _{i}, O_{j}, O_{k}, O_{l} represent unassigned sub-cell optical densities;calculating four summed optical densities (T _{1}, T_{2}, T_{3}, T_{4}) from said optical density values S_{1}, S_{5}, S_{4} and S_{2} such that:T T T T arranging said four summed optical densities T _{1}, T_{2}, T_{3} and T_{4} in the order of their magnitudes and relabeling said summed optical densities as T_{i}, T_{j}, T_{k} and T_{l} respectively, such that T_{i} >T_{j} >T_{k} >T_{l} ;relating T _{i}, T_{j}, T_{k} and T_{l} to the ordered optical densities T_{1}, T_{2}, T_{3}, T_{4} such that the subscripts i, j, k, l are identified as each being one of the numbers 1, 2, 3, 4; anddetermining the estimated optical densities for the sub-cells O _{1}, O_{2}, O_{3} and O_{4} by assigning the values O_{i}, O_{j}, O_{l} to the sub-cells O_{1}, O_{2}, O_{3}, O_{4} based upon the above determined identities of i, j, k, l.Description This is a continuation, of application Ser. No. 020,055, filed on Mar. 13, 1979, now abandoned. This invention relates to a method of restoring a picture cell by estimation with high density in a copying machine. FIG. 1 shows a picture consisting of nine equal square picture cells obtained by sampling a copying original. Heretofore, in restoring the central picture cell X by estimation, the estimation is carried out by approximation over linear polynominals including the density data of the eight picture elements A, B, C, D, E, F, G and H surrounding the central picture cell X. The estimation coefficients of the picture cells B, D, E and G are about 0.5, and those of the picture cells A, C, F and H are about -0.25 for Japanese and European languages if they are of a sentence pattern. Therefore, in estimating the central picture element X, there is no substantially great difference in picture quality between the case where all of the picture cells A through H are utilized and the case where only four picture cells B, D, E and G are utilized. This is due to the mutual relations between the central picture cell X and the surrounding picture cells A through H. In other words, the estimation is greatly affected by the picture cells B, G, D and E which are positioned above, below, at the left-hand side and at the right-hand side of the central picture cell X, and is not so affected by the remaining picture cells A, C, F and H. In view of the foregoing, an object of this invention is to provide a method of restoring a picture cell by estimation in which the number of picture cells utilized for the estimation is reduced, which contributes to simplification of the algorithm of restoring the picture cell by estimation. Another object of the invention is to provide a method of restoring a picture cell by estimation by which the construction of a copying machine is simplified and the manufacturing cost thereof can be reduced. The novel features which are considered characteristic of this invention are set forth in the appended claims. This invention itself, however, as well as other objects and advantages thereof will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. In the accompanying drawings: FIG. 1 is an explanatory diagram showing picture cells forming a picture sampled and for a description of a conventional method, which has been already referred to; FIG. 2 is an explanatory diagram for a description of a method of restoring a picture cell by estimation according to the invention; FIG. 3 is a flow chart showing algorithm according to the invention; and FIG. 4 is a block diagram showing a picture cell restoring device for realizing the flow shown in FIG. 3. FIG. 2 shows five picture cells out of nine picture cells forming a picture, which are obtained by sampling a copying original. The five picture cells are utilized in a method of restoring a picture cell by estimation according to this invention. The picture cell to be restored is positioned at the center of the five cells and is designated by reference character S The picture cell S The algorithm in restoring the central picture cell by estimation is as follows: (1) The following equations are calculated: ##EQU1## where S (2) Then, the central picture cell S When the quantized picture cell S (4) Then, with O (5) As a result of this subtraction, if S (6) With O (7) As a result of this subtraction, if S (8) O (9) Completion The flow of the above-described algorithms (1) through (9) is as indicated in FIG. 3. These algorithms are carried out for the entire surface of an original to be copied, but are not effected for the end portions of the original. FIG. 4 is a block diagram showing a picture cell restoring device for realizing the flow indicated in FIG. 3. The picture cell restoring device comprises: an address counter 1 for counting the absolute address of the central picture cell S The picture cell restoring device further comprises: a black picture cell generating circuit 7; and a white picture cell generating circuit 8. When the density level of the picture cell S As is apparent from the above description, according to the invention, it is unnecessary to use all of the eight picture cells to restore the central picture cell unlike the conventional method. That is, the aimed picture cell can be restored by estimation only with four picture cells above, below, right and, left readily when compared with the eight-picture-cell method. This will contribute to simplification of the copying machine and to reduction in the manufacturing cost thereof. Patent Citations
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